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authorJosef Bacik <josef@redhat.com>2012-03-09 09:51:43 -0500
committerChris Mason <chris.mason@oracle.com>2012-03-26 16:51:08 -0400
commit115391d2315239164e400a8259b26392afccf3bd (patch)
tree83f6bd7698b5bfddbe3be57d6411a120eced2399 /fs/btrfs/extent_io.c
parent4f2de97acee6532b36dd6e995b858343771ad126 (diff)
Btrfs: only use the existing eb if it's count isn't 0
We can run into a problem where we find an eb for our existing page already on the radix tree but it has a ref count of 0. It hasn't yet been removed by RCU yet so this can cause issues where we will use the EB after free. So do atomic_inc_not_zero on the exists->refs and if it is zero just do synchronize_rcu() and try again. We won't have to worry about new allocators coming in since they will block on the page lock at this point. Thanks, Signed-off-by: Josef Bacik <josef@redhat.com>
Diffstat (limited to 'fs/btrfs/extent_io.c')
-rw-r--r--fs/btrfs/extent_io.c10
1 files changed, 8 insertions, 2 deletions
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 0381b6007ae4..0f74262911be 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -3750,7 +3750,7 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
}
if (uptodate)
set_bit(EXTENT_BUFFER_UPTODATE, &eb->bflags);
-
+again:
ret = radix_tree_preload(GFP_NOFS & ~__GFP_HIGHMEM);
if (ret)
goto free_eb;
@@ -3760,7 +3760,13 @@ struct extent_buffer *alloc_extent_buffer(struct extent_io_tree *tree,
if (ret == -EEXIST) {
exists = radix_tree_lookup(&tree->buffer,
start >> PAGE_CACHE_SHIFT);
- atomic_inc(&exists->refs);
+ if (!atomic_inc_not_zero(&exists->refs)) {
+ spin_unlock(&tree->buffer_lock);
+ radix_tree_preload_end();
+ synchronize_rcu();
+ exists = NULL;
+ goto again;
+ }
spin_unlock(&tree->buffer_lock);
radix_tree_preload_end();
goto free_eb;